RechercherDomaineTitre

UNIVERSITY OF CALIFORNIA RIVERSIDE Stability of ...
UNIVERSITY OF CALIFORNIA
RIVERSIDE
Stability of Dryland Production of Cowpeas
(Viqna unsuiculata (L.) Walp.)
with Varietal Intercrops
A Thesis submitted in partial satisfaction
of the requirements for the degree of
Master of Science
in
Plant Science
bY
Samba Thiaw
December, 1990
Thesis Committee:
Professor
Anthony E. Hall, Chairman
Professor
Jodie S. Holt
Professor
Giles J. Waines
The thesis of Samba Thiaw is approved:
University of California, Riverside
December, 1990
ABSTRACT OF THE THESIS
Stability of Dryland Production of Cowpeas
(Vicna unsuiculata (L.) Walp.)
with Varietal Intercrops
bY
Samba Thiaw
Master of Science, Graduate Program in Plant science
University of California, Riverside, December, 1990
Professor Anthony E. Hall, Chairman
Low and variable yields constrain grain production
under rainfed conditions in semiarid zones. These problems
are particularly acute in northern Senegal where grain
Y
production is limited by low and variable rainfall. This
study was conducted to determine whether varietal inter-
crops of cowpea are better adapted to semiarid climates
and infertile soils than sole crops of cowpea. The same
experiment was conducted over two years in three locations
in northern Senegal which have contrasting rainfall and
soi1 fertility. The locations are representative of the
major cowpea production zones of Senegal. Two varietal
intercrops and six cultivars were grown in a randomized
complete block split plot design with 4 replications. The
varietal intercrops consisted of alternating rows of a
vii
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w%-I
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- . - - - . I ” U U I I I ” ‘ , . U I I I - - - - , - -
M-I-III--

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..-u~*l~i
medium cycle spreading cultivar (58-57) and an early erect
cultivar (Bambey 21 or CB5). The six cultivars grown as
sole crops included the three cultivars used in the inter-
trop and three others with spreading (N'diambour and
Mougne) or semierect (Tvx 3236) growth habit that are well
a'dapted to northern Senegal. The split plots consisted of
application of fertilizer (150 kg/ha of 6:20:10, N:
P2O5:K2O) and a control where no fertilizer was applied.
Grain and hay yield responded significantly to fertilizer
application at the two drier locations, Thilmakha and
Louga, but not at Bambey which according to soi1 analysis
had higher levels of nitrogen and phosphorus. There were
no genotype x fertilizer interactions. Cultivar and inter-
trop comparisons were based on mean yields across the soi1
fertility treatments. The varietal intercrops were more
effective at Thilmakha and Louga than the sole crops. In
these drier and less fertile locations the varietal inter-
crops had the highest mean yields of grain and hay, the
highest land-use efficiency (LERs of 1.42 for grain and
1.50 for hay), and above average stability. In the wetter
and more fertile location (Bambey), the performance of the
varietal intercrop was intermediate, and the dense canopy
made it difficult to harvest the grain of the two culti-
vars in the intercrops separately. These studies demon-
strated that intercrops of early erect and medium cycle
spreading cowpeas cari have higher and more stable
viii
Ije
- - ~ r - - D , 1 P * i r * . . ~ * “ . a r - - - - - - - - - -

----
-----“.-.”
-i
t
yields of grain and hay than sole crops, in conditions
where drought and infertile soi.1 limit trop production.
ix
TABLE OF CONTENTS
page
ACKNOWLEDGEMENTS......"....................~.~...~~
.
ABSTRACT ..................................
..t ..... vii
TABLE OF CONTENT .................................. X
LIST OF TABLES .....................................
xi
LIST OF FIGURES...................................xii i
INTRODUCTION AND LITERATURE REVIEW...............: L
MATERIALS AND METHODS......................< ... ...8
Cultural practices .......................... ...8
Experimental design......................*.....l:!
RESULTS AND DISCUSSIONS.........................."l( 5
Weather conditions..............................1f
5
Response to fertilizer..........................2: 1
Genotypic yield response........................:32 Z
Land-use efficiency.............................3f 5
Stability and adaptation of the genotypes.......4 4
LITERATURE CITED..................................S4
X
--_
m.“.--
-m-m-------.-
. ^ _.-..
-‘r-l-
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LIST OF TABLES
Table 1
Sowing and harvesting dates for cowpea
and rainfall amount and duration at
Bambey, Louga and Thilmakha for each year......ll
Table 2
Origin and characteristics of the cowpea
cultivars used...............................,.l3
Table 3
Soi1 minera1 nutrient content in the
O-20 cm depth at three locations in
Senegal.................................~....,.28
Table 4
Leaf blade mineral. nutrient content of
cowpea in senegal.......................29
Table 5
Mean grain yield for a11 treatments in
control and fertilized plots at Bambey,
Thilmakha and Louga.....................a...m..30
Table 6
Mean hay yield of a11 treatments in
control and fertilized plots at Bambey,
Thilmakha and Louga...................*.....*..31
Table 7
Treatment grain yield of cowpea at three
locations in Senegal..................*....."..34
Table 8
Mean grain and hay yields of cowpea at
Bambey and Thilmakha plus louga combined
averaged over 1988 and 1989.................*.*35
Table 9
treatment hay yield of cowpea at three
locations in Senegal..................*.....*..36
Table 10 Yield component for three cultivars of
cowpea grown in 1989 in Senegal: Number
of peduncles and pods per plant and pods
per peduncle..........................~.....~,.38
Table 11 Mean values for LER and ATER for grain
and hay yields of cowpea across fertilizer
and years at Bambey, Thilmaka and Louga......*.40
Table 12 Partial LERs for grain for each component
cowpea cultivar in the varietal intercrop
during two years in each location..............42
Table 13 Partial LERs for hay for each component
cowpea cultivar in the varietal intercrop
during two years in each location............ti.43
c
xi
..*
” >,. . “*--lull*IL-‘.~*l..~-~---I---
-
-
--_.--
Table 14 Linear regression analysis over six
environments (3 locations x 2 years) for
treatment grain yield versus environmental
mean grain yield in cowpea.....................45
Table 15 Linear regression analysis over six
environments (3 locations x 2 years) for
treatment hay yield versus environmental
mean hay yield in cowpea.......i.............,..+.46
xii
LIST OF FIGURES
Figure 1
Central and northern peanut basin in
Senegal. Experiments were conducted at
Bambey, Thilmakha and Louga............-...*..9
Figure 2
Mean rainfall and evaporation for every
ten day interval from sowing at Bambey
and Louga 1988. ETP = Evaporation from
Class A Pan...................................17
Figure 3
Mean rainfall and evaporation for every
ten day interval from sowing at Bambey
and Louga 1989. ETP = Evaparation from
Class A Pan..........................~.,....~.l9
Figure 4
Mean rainfall for every ten day interval
from sowing at Thilmakha in 1988 and :1989.....21
Figure 5
Mean maximum and minimum air temperature
for every ten day interval
from
sowing at Bambey in 1988 and 1989.............24
Figure 6
Mean maximum and minimum air temperature
for every ten day interval from sowing
at Louga in 1988 and 1989.....................26
Figure 7
Relationship of cowpea cultivar adaptation
(regression coefficient) to cultivar mean
grain yield in a11 environments. Regression
coefficieny (b) was taken from analysis shown
in Table 14...................................48
Figure 8
Relationship of cowpea cultivar adaptation
(regression coefficient) to cultivar :mean hay
yield in a11 environments. Regression
coefficient (b) was taken from analysis shown
in Table 15..................................*50
xiii
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INTRODUCTION AND LITERATURE REVIEW
The cropping systems that are most effective in semi-
arid zones must be adapted to the soil, biotic and cli-
matic conditions. In these zones, yields are generally low
and variable as a conseguence of limited and variable
rainfall and other constraints.
In semiarid regions of Senegal, most farmers do not
have water for irrigation and they must rely on rain to
produce their food and cash crops. In the Sahelian and
Sudanian zones of Senegal, the average rainfall provides
sufficient moisture for a 60 to 100 day cropping season
which is followed by a long dry season (Dancette and Hall,
1979). Drought often occurs at different times during the
cropping season, substantially reducing trop production.
Cowpea (Visna unsuiculata (L.) Walp.) is a warm sea-
son trop that has been grown in Senegal for thousands of
years (Ng and Marechal, 1985). Formerly, it was planted in
home gardens or intercropped with cereals or other crops.
Spreading, late flowering types of cowpea, which were pho-
toperiod sensitive, were mainly used. During the last
thirty years, new cultivars have been developed with early
and medium maturity and erect or spreading growth habit.
These cultivars have different levels of drought resis-
tance depending on the stage of plant development when the
drought occurs (Hall and Patel, 1985).
Cowpea is an important trop in the northern peanut
1
c
basin in Senegal due to its ability to produce food under
conditions of drought and infertile soils where the other
s,taple crops, Pearl millet, sorghum and peanut have, in
some years, produced virtually no food. For subsistence
farmers under conditions of variable drought and other
soi1 and biotic constraints, yield stability ma'y be more
important than high yield. Cropping systems of semiarid
West Africa were reviewed by Fusse11 and Serafini (1985)
who concluded that Pearl millet/cowpea intercrops coulld
enhance and stabilize yields compared with sole crops.
However, C. Dancette evaluated Pearl millet/cowpea inter-
crops in the semiarid zone of Senegal over a five year
period and concluded that sole crops were most effective
in the drier zone (NIdoye et al. 1984).
Presently, more than 90% of the cowpeas cultivated in
the semiarid region of Senegal are grown as sole crops.
Varietal intercrops, combining morphologically and pheno-
logically contrasting cultivars of cowpea, could enhance
.x
yield stability and contribute to food requirements (Hall,
1988).
In northern Senegal, farmers usually experience
food shortages just before the Pearl millet and tradi-
tional cowpea cultivars are ready to harvest. Cowpea cul-
tivars with earlier maturity cari provide food and cash
during the traditional period of hunger, as well as
greater grain yield than later maturing cultivars when the
rainy season is very short. Medium maturing and spreading
2
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cultivars cari produce more grain and hay than the early
erect cultivars when the rainy season is of adequate dura-
tion. On-farm studies in Senegal have demonstrated that
fanners like to grow both types of cowpeas: the early
erect cultivars and the medium cycle spreading ones
(N'diaye, 1987; Bal, 1988). Possible advantages from var-
ietal intercrops consisting of alternating rows of these
two types of cultivars may be seen from the following
example. Where drought occurs early in the season, the
early cultivar may senesce, but if rains resume, a late
maturing cultivar grown in a varietal intercrop could com-
pensate by spreading into the space made available by the
senescence of the early cultivar.
Few studies were discovered in the literature in
which the stability of varietal intercrops was evaluated.
Rattunde et al. (1988) combined morphologically and pheno-
ltogically different cultivars of groundnut as mixed inter-
trop and row intercrop. They found that the highest pod
yields of the mixed intercrop and row intercrop failed to
exceed the yield of the best sole trop at low and high
densities. They concluded that future experimentation with
groundnut mixtures in the tropics should focus on stabil-
.ity rather than maximization of yield.
The performance of intercrops is often evaluated by
use of Land Equivalency Ratio or LER. LER is the relative
land area under two sole crops that would be required to
il.
3
produce the same yield as the intercrop (Hiebsch and
McCollum, 1987). It gives a valid estimate of efficiency
when both intercrop and monoculture are under the same
level of management and monocultures are under optimal
population levels. Nageswara et al. (1990) evaluated the
performance of intercropping short and long duration
groundnut genotypes in environments subjected to end-of-
season-droughts. The intercrop treatments resulted in LERs
of 0.93 to 1.25 with a mean of 1.1 for pod yielld and 0.99
to 1.15 with a mean of 1.1 for total biomass at the end of
the season. They concluded that growing groundnut geno-
types with different season length reguirements as an
intercrop is a better solution to variable season length
tlhan simply spreading the risk by growing a range of geno-
types as sole crops.
Preliminary studies in Senegal by Diouf (1986) and
Diagne (1986) also demonstrated that varietal intercrops
cari be more effective than sole crops. Diagne (l.986) com-
pared varietal intercrops of cowpea consisting of alter-
nating rows of an early erect cultivar and a medium Cyc:le
spreading cultivar with sole crops of the same cultivars.
In the first year, the LER for grain yield was only
slightly greater than unity (1.08). In the second year,
the varietal intercrop made much more efficient use of the
land than the sole trop with an LER for grain of 1.41
(Diagne, 1986). In addition, the varietal intercrop pro-
4
duced 20% more grain than the highest yielding sole trop
and 58% more grain and 40% more hay than the average
yields of the sole crops. The studies described above were
a11 conducted at Bambey in the wetter part of the semiarid
zone of Senegal. It is particularly important to evaluate
varietal intercrops over a range of drier environments
which exhibit more extreme and more variable levels of
drought.
Hiebsch and McCollum (1987) conducted an extensive
review of the literature on intercropping. They concluded
that large values of LER occurred when components of the
intercrop had large differences in time of maturity and
when leguminous crops were grown in soi1 with low supplies
of nitrogen (Hiebsch and McCollum, 1987). These conclu-
sions would apply when a cowpea varietal intercrop of
early and late maturing cultivars is grown in the infer-
tile soils in the drier part of the semiarid zones of
Senegal. Fertilizer response studies have demonstrated
that in the northern peanut basin, deficiencies of
nitrogen and phosphate limit cowpea production,, whereas in
the central peanut basin deficiencies of potassium are
also present (Nicou and Poulain, 1969). Hiebsch and McCol-
lum (1987) also proposed a method which is more effective
than LER to evaluate the biological efficiency of inter-
~crops, the Area x Time Equivalency Ratio (ATER). ATER dif-
fers from LER in that it adjusts for any diffe,rences in
5
+e
occupancy duration of the land by the components of the
intercrop. Yield response to variation in environment due
to years and locations is also an important criterion ta
assess the adaptation of cropping systems or cultivars to
semiarid environments. Long-term average yield and yie:Ld
stability are important indices of adaptation (Hall et
al., 1979). Several methods are available to evaluate
yield stability (Blum, 1988), but they cari make different
predictions concerning the relative stability of the same
set of cultivars (Hall et al., 1979).
A widely used method to evaluate stability consists
of the regression of the yield of individual cultivars
against an environmental index consisting of the mean
yield of a11 cultivars in the tria'1 using data from dif-
ferent locations and years (Finlay and Wilkinson, 1963).
Linear regression, as used by Eberhart and Russe1 (1966),
would appear to be more appropriate than the logarithmic
regression used by Finlay and Wilkinson, (19631, however,
because it provides equal weighting to the different envi-
ronments. The final step consists of plotting the regres-
sion coefficient against the overall mean yield of the
cultivars (Finlay and Wilk;inson, 1963). Cultivars with
high mean yields and regression coefficients less than or
close to unity would be considered to be broadly adapted
to a11 environments experienced in the trials, whereas
cultivars with very low regression coefficients would tend
6
-.
L
to be adapted to the test environments with low yield
potential (Blum, 1988). Eberhart and Russe1 (1966) pointed
out that the deviations from regression of individual cul-
tivars provided an additional measure of stability, but
this parameter is not a measure of general stability (Hall
et al., 1979). Multiline mixtures of soybean bave been
compared with pure lines. In one study, certain mixtures
had greater stability and higher yields than the pure
lines (Schutz and Brim, 1971). The four cultivars used by
Shutz and Brim (1971) had substantial differences in matu-
rity date (29 day range), but only modest differences in
. .
morphology; they were upright and determinate. In another
study, there were no significant differences in yield and
regression coefficients between mixtures and pure lines
(Walker and Fehr, 1978). Walker and Fehr (1978) used many
pure lines but the maturity dates of the lines were within
a-lO-day range and the morphologies of the lines were sim-
ilar. F'or mixtures or intercrops to have greater stability
than pure lines grown as sole crops, the component lines
may have to exhibit substantial differences in morphology
and phenology.
The main objective of this study was to compare the
average yield, yield stability and efficiency of land use
of varietal intercrops and sole crops of cowpea grown in
several locations with contrasting levels of drought and
soi1 fertility.
"I
7
MATERIALS AND METHODS
During the summers of 1988 and 1989, the same exper-
iment was conducted in three semiarid locations in Senegal
West Africa with contrasting rainfall (Figure 1 and Table
The climate of Senegal has one rainy season lasting
? ?? ?
from two to five months. Al1 food and cash crops are grown
during this season. The three experimental sites were Bam-
bey, Louga and Thilmakha (Figure 1). At Bambey the exper-
iment was conducted on a deep, slightly leached, tropical
ferruginous soil, called a llDiorVV soil. Based on the
International Soi1 Science Classification, this soi1 has
7% clay, 3% silt, 68% fine Sand, 22% coarse Sand, and
little variation in texture in the first 2 m. T:he volumet-
rit moisture content at field capacity is 1652%.
Using
t:he United States Department of Agriculture (USDA) Soi:1
Taxonomy, this soi1 is classified as a Ustipsamment (Hall
and Dancette, 1978). Louga and Thilmakha are located in
the northern part of the peanut basin and the soils are
sandy with a low percentage of clay (3%) and a low field
capacity (8%). The pH of the soils is neutral to acidic
although soils at Louga and Thilmakha are more acidic than
at Bambey.
Cultural oractices
Fields were chosen where Pearl millet had been grown
the previous year and they were plowed during the dry sea-
son in May. Al1 trials were hand planted when the soi1 was
8
E
Figure 1.
Central and northern peanut basin in
Senegal.
Experiments were conducted
at Bambey, Louga, and Thilmakha.
9
Table 1.
Sowing and harvesting dates for cowpea and
rainfall amount and duration at Bambey
c
Louga and Thilmakha for each year.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..“............~*..*~.
Location
Year
Rainfall
Dates of
amount days
sowing harvesting
. . . . . ..a.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...“.
(mm)
(no.)
Bambey
1988
6391 50
8-4-88
10-14-88
Thilmakha
1988
409 33
8-4-88
10-5-88
Louga
1988
442 32
7-30-88
10-14-88
Bambey
1989
805 42
6-28-89
9-15-89
Thilmakha
1989
550 34
7-8-89
9-20-89
Louga
1989
470 31
7-8-89
9-30-89
c
11
e
sufficiently wet from natural rainfall to insure germina-
tion and plant establishment (Table 1). Two seeds of six
c'owpea cultivars were planted per hi11 and hills with zero
emergence were replanted o:ne week later. After seedling
emergence, the hills were ,thinned to one plant per hi11 in
a11 locations. Weeds were removed about 15 days after
emergence, when the cowpea seedlings were well estab-
lished. The trials were hand weeded with a hoe three times
during the cropping season.
Chemical control of insects was maintained in a11
three locations. Hairy caterpillar (Amsacta molonevi DRC)
,x
is particularly damaging to the Young seedlings and cowpea
aphid (Anhis craccivora Koch) damages the meristems and
tender stems. Both insects were controlled by Thimul 35
applied at the rate of 2.5L per ha (the active ingredient
is endosulfan at 800 g/ha). The other major insect was the
flower thrip (Mesalurothris siostedti Trybom) which was
controlled with Decis appl.ied at the rate of 25g per ha
(the active ingredient is deltamethrine at 15 g/ha).
Exnerimental desisn and treatments
Six cowpea cultivars (Table 2) and two varietal
intercrops provided eight treatments which were planted in
a randomized complete block split plot design. The eight
treatments were in the main plots and two fertilizer lev,-
els were in the the sub-plots. The main plot consisted of
:L2 rows, each 5 m long. The distance between rows was 50
12
Table 2.
Origin and characteristics of the cowpea cul-
tivars used.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..~....
Cultivars
Origin
Period from
Growth
Weight,/
sowing to 50%
habit
seed
flowering
..*................ . ..*......... . . . . . . . . . . . . . . . . . . . . . . . .
Wys)
(mg)
n
58-57
Senegal
44
spreading
118
N'diambour Senegal
44
spreading
177
Mougne
Senegal
46
spreading
129
Tvx 3236
IITA, Nigeria
45
semi-erect
106
Bambey 21
Senegal
41
erect
141
California USA
38
erect
176
Blackeye 5
(CB5)
13
cm for a11 cultivars in a11 locations. Within the rows the
distance between hills varied from 25 cm for the erect
cultivars to 50 cm for the spreading ones. A semi-erect
cultivar, Tvx 3236 was sown at 50 cm within rows. The two
intercrop treatments consisted of an eaply-erect cultivar
I3ambey 21 or California Bl.ackeye No. 5 (CB5), and a
medium-maturity spreading cultivar, 58-57, sown in alter-
nate rows. The four central rows of each sub-plot were
harvested at the end of the rainy season (Table 1) to
determine dry weight yields of grain and hay.
Prior to applying fertilizer, soi1 samples were taken
at Bambey, Louga, and Thillmakha in the O-20 cm depth for
analysis. The concentrations of total N, P (P2O5), and
exchangeable K (K20) were determined. One of the split
plots received fertilizer which was broadcast and incor-
porated at the rate of 150 kg/ha of 6-20-10 (N:P205:K20).
Fully expanded, mature leaves were sampled at mid-bloom
(between 35 and 45 days after sowing) from the cultivars
58-57, Mougne, Bambey 21, and CB5 in both the control and
the fertilized plots. Leaf blades were ground and passed
through a 20 cm-mesh screen and digested by the rapid nit-
ric/perchloric acid method. The K and micro-nutrient (Fe,
CU , Zn and Mn) contents in the leaves were determined by
atomic absorption spectrophotometry. The level of P in the
l.eaf blades was measured using the modified colorimetric
method of Berg and Gardner (1978). At harvest, the number
14
of peduncles, pods per plant and pods per peduncle were
dletermined for the cultivars 58-57, Bambey 21 and CB5.
Weather stations at Bambey and Louga provided data on
rainfall, daily pan evaporation (US Weather Bureau Class
A) t and the daily maximum and minimum shelter air tempera-
turcs. At Thilmakha, only rainfall was measured.
c
15
RESULTS AND DISCUSSION
Weather conditions
There was more rain in 1989 than 1988 and Bambey
received more rain over moire days than Thilmakha and Louga
(Table 1). Comparison of rainfall and pan evaporation
indicated that the rainfall in 1988 would have supported a
70-day growing season at Elambey, but only a 60-day growing
season at Louga (Figure 2). A drought occurred at Louga
during the fourth ten-day interval when the cowpeas were
in the early flowering stage. In 1989 there was sufficient
rain to support a 90-day growing season at Bambey, but
only a 70-day growing season at Louga where the sandy soi1
has limited ability to store water in the root zone (Fig-
ure 3). An extreme drought ocurred at Louga during the
second and third ten-day intervals after sowing when the
cowpea was in the late vegetative stage. The rainfall at
Thilmakha (Figure 4) was more similar to the rainfall at
ILouga than at Bambey for both years (Figures 2 and 31,
with Thilmakha receiving :33 mm less rain than Louga in
:L988 and 80 mm more rain in 1989 (Table 1). The daily eva-
poration data at Thilmakha would have been similar to the
data obtained at Louga. The daily mean pan evaporation was
lnigh and dependent on the rainfall. At Bambey the mean
evaporation from sowing to harvesting was 6.4 mm and 6.1
:mm in 1988 and 1989, respectively, whereas at Louga it was
6.0 and 6.1 mm from sowing to harvesting for the two
16
Figure 2.
Mean rainfall and evaporation for
every ten day interval from sowing at
Bambey and Louga in 1988.
ETP = Evaporation from Class A Pan.
17
P
I
23 !-
LOUGA
1 8
Figure 3.
Mean rainfall and evaporation for every
ten day interval from sowing at Bambey
and Louga in 1989.
ETP = Evaporation from Class A Pan.
19
IG ,
j
/
i
!
,
u
. ?J -
TZN CAY INTERVALS FROM SO’NING
Figure 4.
Mean rainfall for every te? day
inter-val from sowing at Thilmakha
in 1988 and 1989.
i
3ol--------I
l THILMAKHA
1988
-1
23 -
WL
ca RAIN
4:
i
/
I
4
THILMAKHA
**
r i LTEN DAY INTERVALS FROM SOWING
years. The daily maximum and minimum air temperatures
averaged over a ten day period were similar in 1988 and
:L989 at Bambey (Figure 5) and Louga (Figure 6) ,, Daily max-
imum and minimum air temperatures were uniformly high,
averaging 33 and 24 OC, respectively, at Bambey and 34 and
;24 OC, respectively, at Louga.
Resnonse to fertilizer
Soi1 analysis conducted in 1989, prior to applying
the fertilizer, showed that total N and P were substan-
tially lower and more deficient at Thilmakha and Louga
than at Bambey (Table 3). The level of exchangeable K was
similar in the three locations. No significant differences
were observed between the fertilized and the control
treatments in leaf blade :mineral content, but significant
ldifferences were observed between locations in a11 miner-
als except P (Table 4). The levels of P in the leaf blades
.were intermediate and not significantly different between
the three locations despite the higher P content in the
soi1 at Bambey. The K level was lower at Thilmakha than at
the two other locations. Among the micro-nutrients, Mn was
higher at Louga and Thilmakha, possibly reflecting a
lower soi1 pH than at Bambey (Table 4).
The fertilizer treatment resulted in significantly
higher yields of grain (Table 5) and hay (Table 6) than in
control plots at Thilmakha and Louga but not at Bambey.
Bambey had higher soi1 N in the contra1 plots than did the
*
23
Figure 5.
Mean maximum and minimum air temperature for
every ten day interval from sowing at Bambey
in 1988 and 1989.
y.
I
25
26
Table 3.
Soi1 minera1 nutrient content in the O-20 cm
d.epth at three locations in Senegal.
. ..*.....................................*.......**~
Minera1 content
Location
Bambey
Thilmakha
Louga
."...............
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
total N (g/kg)
CI.33
0.18
0.19
c v
C%l
8.67
24.69
10.14
total P (gjkg)
0.31
0.23
0.18
C V
C%l
3.80
19.04
15.74
exch. K (meq/lOOg)
3.17
3.06
3.11
C V
(%)
5.74
15.97
9.14
. . . . . . . . . . ..*.................. . . . . . . . . . ..*......e..
cv = coefficient of variation.
Exch. K = exchangeable potassium.
28
c
P
Table 4.
Leaf blade minera1 nutrient content of cowpea
in Senegal in 1989.
. . . . . . . . . . . . . . . . . . . . . . . . ..s................... ..e.“. . . . . . .
Location
Minera1 concentration
M n
Fe
Zn
C U
K
P
.........................................................
....... (g/Mg) ...........
. - (g/'kg) . -
Bambey
281
145
28
12 13.1
3.2
Louga
488
260
30
9 12.0
3.3
Thilmakha
477
134
24
8 8.2
2.7
LSD (0.05)
70
31
2
2 1.0
ns
signif.
***
***
***
***
***
ns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*.............. . ? ? ? ?????
*** = significant at p = 0.005
ns = non signicant at p = 0.05
LSD for location
29
Table 5.
Mean grain yield of cowpea for a11 treatments
in control and fertilized plots at Bambey,
Thilmakha and Louga.
.*.............
. . . . . . ..o....................*.....*....
Treatment
Bambey
Thilmakha
Louga
1988
:L989
1 9 8 8
1 9 8 9
1988
1989
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*.~...*....
. . . . . . . IV . . . . . . . . (kg/ha).....+..........
Control
1394
:L334
671
599
616
501
Fertilized
1438
:L399
930
933
875
575
Yield diff.
44
5
259
334
259
74
Fertility
ns
11s
***
***
***
*
LSD (0.05) -
.m
67
53
60
54
gen.x fert.
ns
11s
ns
ns
IIS
ns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . ..*...e......*.*.
Fertility gives the significance between control
and fertilized P:lots
LSD for the control and the fertilized plots
Gen. x fert. interaction between main treatments
(cultivars) and subtreatments (fertility level).
*
***, ns = significant at p = 0.05, p = 0.005
and non significant at p = 0.05, respectively.
30
c
Table 6.
Mean hay yield of cowpea of a11 treatments in
control and fertilized plots at Bambey, Thil-
makha and Louga.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*..*.........*..
Treatment
Bambey
Thilmakha
Louga
1988 1989 1988 1989 1988 1989
. . . . . . . . . . ..*..s . . . . . . . . . . . . . . . . ..*............*.......*.
. . ..a........... (kg/ha)................
Control
2424 4766 530 843 461 847
Fertilized
2437 4642 784 1147 758 956
Yield diff.
13
-~124
254
304
297
109
Fertility
ns
rlS
***
***
***
*
LSD (0.05)
-.
67
72
78
101
.,.........................,...........*........*..........
gen. x fert. ns
11s
ns
ns
ns
ns
Fertility gives the significance between the control
and fertilized plots.
J
LSD for the control and fertilized plots.
Gen. x fert. interaction between main treatments
(cultivars) and subtreatments (fertility levels).
*r ***, ns = significance at p = 0.05, p = 0.005, and
non significant respectively.
31
other two locations (Table 3). Consequently the yield
responses at Thilmakha and Louga may have been due to the
small amount of N (9 kg/ha) in the fertilizer treatment.
The studies of Agboola (1.978) in Nigeria demonstrated that
cowpea yield cari respond to application of 10 kg/ha of N
when the percentage of soi1 organic matter is as low as
0.5 or l.O%, but not with 2% or greater organic matter.
The soi1 organic matter was estimated to be 0.66%, 0.36%
and 0.38% at Bambey, Louga and Thilmakha, respectively.
Under the economic conditions prevailing in Senegal, the
average yield response to starter fertilizer observed at
Louga and Thilmakha would have been profitable. The geno-
type x fertilizer interaction was not significant in
either year at any location for either grain (Table 5) or
hay yield (Table 6). This indicates that triais to
evaluate cultivars or varietal intercrops should give sim-
ilar genotypic rankings leither with or without fertilizer,
Since there was no genot~ype x fertilizer interaction, in
the subsequent analyses yields are examined which repre-
sent the average across the control and fertilized treat-
ments.
Genotvpic vield response
The overall grain and hay yields were higher at Bam-
bey during 1988 and 1989 than at Thilmakha and Louga
(Tables 5 and 6). Shoot biomass (grain plus hay) was posi-
tively correlated with seasonal rainfall (r2 = 0.93, P
32
/-
=0.002) indicating that the higher yields at Bambey were
associated with wetter conditions. The higher soi.1 fertil-
ity at Bambey was an additional factor contributing to
yield.
Despite the high rainfall in 1989 (Table l), the
overall grain yield was higher in 1988 in a11 locations,
possibly due to a more uniform distribution of the rain in
1988. The disease and insect pressures were also different
from one location to another. Plots at Bambey suffered a
severe aphid infestation coupled with mosaic virus infec-
tion of 58-57 and N'diambour in 1988, while Louga and
Thilmakha suffered from hairy caterpillar in 1989.
The treatments differed significantly in grain pro-8
duction except at Thilmakha and Louga in 1989 (Table 7).
Highest mean grain yields at Bambey (Table 7) were
achieved by sole crops of intermediate (Tvx 3236), erect
(Bambey 21) and spreading (N'diambour)
cultivars. The
genotype x year interaction was highly significant at Bam-
:bey for both grain and ha,y but not at Thilmakha and Louga,
'This indicated that the average ranking of the cultivars
was not the same from year to year at Bambey. Analysis of
the data from Thilmakha a.nd Louga indicated no significant
genotype x location interactions (Table 8) SO it is appro-
priate to evaluate the mean values across these locations.
Mean grain and hay yields for Thilmakha and Louga combined
were highest for the varietal intercrops (Table 8).
The treatments diffe:red significantly in hay produc-
33
Table 7.
Treatment grain yield of cowpea at three
locations in Senegal.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Treatment
Location
Bambey
Thilmakha
Louga
1988
1989
1988
1989
1988
1989
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*.......
. . . . . . . . . . .
. . . . . . . . . . . . . . . (kg/ha)......"..........
58-57
1171
9 0 0
697
834
831
672
Nldiambour
1515
14!21
910
659
a94
491
Mougne
1220
14179
662
669
750
478
Tvx 3236
1472
21.84
450
669
375
550
Bambey 21
1416
1783
657
678
600
450
CB5
1580
a 7 9
890
637
719
316
58-57/B. 21
1346
1:t72
1010
ii84
769
625
5a-57/CB5
1607
1167
1127
797
1025
722
mean
1416
1367
801
766
745
538
LSD (0.05)
266
3 68
334
ns
323
ns
signif.
*
* :k
**
ns
*
ns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. ..*......*..
*r **, ns = significant at p = 0.05, p = 0.01,
and non signiflcant, respectively.
34
Table 8.
Mean grain and hay yields of cowpea at Bambey
and Thimakha plus Louga combined averaged over
1988 and 1989.
. . . . . . ..*.............*...................................
Treatment
Location
Bambey
Thilmakha + Louga
grain
hay
grain
haY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . (kg/ha)................
58-57
1036
3674 758 766
N'diambour
1468
4388 738 908
Mougne
1349
3982 639 752
Tvx 3236
1828
3998 510 495
Bambey 21
1600
2842 596 740
California
1230
2276 640 615
Blackeye 5
58-57/Bambey 21
125!3
3500 896 1100
58-57/CB5
138'7
3872 917 952
mean
1391
3567 712 787
LSD (0.05)
233
818 130 122
gen. x year
***
***
gen. x locat.
ns
ns
. . . . . . . . . . . . . . . . . . . . . . ..*.....................*....
LSD (0.05) gives the level of significance between the
different treatments
*+*, ns = significant at p = 0.005, and non signific:ant
at P = 0.05, respectively
35
tion except at Louga in 1988 (Table 9). At Bambey highest
m.ean hay yield was achieved by a sole trop of the spread-
ing cultivar N'diambour, which also had a high grain yield
(Table 7). The hay yields of the varietal intercrops were
intermediate at Bambey (Ta&ble 9). Mean hay yields for
Thilmakha and Louga combined (Table 8) were highest for
the varietal intercrops and lowest for the erect cultivars
(Bambey 21 and CB5). These data demonstrate that under
water limiting conditions in infertile soils such as at
Thilmakha and Louga, varietal intercrops cari produce
higher yields of grain and hay than sole crops of either
erect or spreading cultiv,ars. At Bambey with higher rain-
fa11 and higher soi1 fertility, intercrops were not as
productive as the sole crops and would be difficult to
c
manage due to the dense canopies that developed.
Yield component data for three contrasting genotypes
in the three locations (Table 10) demonstrate that the
higher yields at Bambey were associated with a greater
number of peduncles and pods. There was little difference
in number of pods per peduncle among locations.
Other
studies with cowpeas under different irrigation treatments
have also shown a strong positive association between
grain yield and the number of pods per plant (Ziska and
Hall, 1983).
Land-use and Bioloaical Efficiencies
Two of the treatments consisted of varietal inter
36
Table 9.
Treatment hay yield of cowpea at three loca-
tions in Senegal.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..~..........."
Treatment
Location
.
Bambey
Thilmakha
Louga
1988
1989
1988
1989
1988
1989
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*............*..
.
.
.
..a..........
(kg/ha).................
58-57
2147
5200
450
1094
546
975
N1 diambour
2995
5787
891
994
762
987
Mougne
2767
5197
512
1122
500
875
Tvx 3236
2660
5337
328
687
294
672
Bambey 21
2477
3206
669
869
650
775
CB5
2016
2537
609
556
600
625
58-57/B. 21
1975
5025
984
1487
669
1262
58-57/CB5
2407
5337
816
1150
894
9 50
mean
2431
4:704
657
995
609
902
LSD (0.05)
654
1.487
356
356
ns
208
signif.
*
3r *
**
**
ns
**
. . . . . . . . . . . . . . . . . . . ..~................................
*, **, ns = significant at p = 0.05, p = 0.01, and
non significant at p = 0.05, respectively.
m/
37
Table 10.
Yield components for three cultivars of cow-
pea grown in 1989 in Senegal.
.a.................. ..,........ . . . . . ..*...........*........
Location
Bambey
Thilmakha
Louga
ped/ pod/ WV @./
WV pod/ ped/ pod/ poW1
plant plant ped plant plant ped
plant plant ped
. . . ..*............... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..o.*
. . . . . . . . . . . . . . . . . . . . . . (no.)..... . . . . . . . . . . . ...*...
C:B5
11
22
2
4
9 2.1
9
20
2.2
58-57 11
16
1.5
6
11 2.1
7
12
1.6
B. 21 14
22
1.6
5
8 1.6
11
13
1.2
mean
12
20
1.7
5
9 1.9
9
15
1.6
CV(%) 15
24
31
1
16 14
22
28
32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...“.....
. . . . . . . . . . . . . . . .
1 = number of peduncles and pods per plant and
number of pods per peduncle.
cv = coefficient of variation.
e
crops with alternating rows of early erect and spreading
cultivars. Their efficiencies of land use were compared
with sole crops of the same cultivars. Mean LER values
(Table 11) showed that thea varietal intercrops had land
use efficiencies for grain and hay that were 55% and 57%
higher, respectively, than the sole crops at Thilmakha,
and 30% and 43% higher, respectively, for grain and hay at
Louga. The advantage of the varietal intercrops was
smaller at Bambey with +15% for grain and +22% for hay
(Table 11). The extent to which the greater droughts and
lower soi1 fertility contributed to the greater LERs at
Thilmakha and Louga, compared with Bambey, is not known.
There was no difference in the LERs of fertilized compared
with control plots at Thilmakha or Louga. In the studies
reviewed by Hiebsch and McCollum (1987) there was a gen-
eral tendency for higher LERs under less fertile soi1 con-
ditions. They also showed that intercrops grown under low
soi1 N had ATER values greater than unity, whereas inter-
crops under high soi1 N had average ATER values close to
unity (Hiebsch and McCollum, 1987). In this study, the
ATER values showed that the varietal intercrops were biSo-
logically more efficient than sole crops of the same cul-
tivars (Table 11). At Thilmakha, the biological efficien-
cies of the intercrops for grain and hay were 30 and 44%
higher, respectively, than the sole crops, while at Louga,
the biological efficiencies for grain and hay were 13 and
39
t
Table 11.
Mean values for LER and ATER for grain and
hay yield of cowpea across fertilizer and
years at Bambey, Thilmakha and Louga.
. . . . . . . . . . . ..*.s...................
. . . . . . . . . . . . . . . . . . ..*.a
Location
Intercrop
LER
ATER
grain
hw
grain
hay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*.......*...........*...**.
58-57/B 21
1.05
1.07
0.97
0.98
Bambey
58-57/CB5
1.25
1.37
1.10
1.15
mean
1.15
1.22
1.06
LSD (0.05)
o,, 19
ns
58-57/B21
1,64
1.67
1.47
1.57
Thilmakha
58-57/CB5
1.38
1.50
1.14
1 . 3 2
mean
1.55
1.57
1.30
1.44
LSD (0.05)
ns
ns
58-57/B21
1.12
1.47
1.06
1.32
Louga
58-57/CB5
1.48
1.40
1.21
9.24
mean
1.30
1.43
1.13
1.28
LSD (0.05)
0.33
ns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*............*...*..
ns = non significant at p = 0.05
LSD(0.05) for the two intercrop treatments
LER = Land Equivalency Ratio.
ATER = Area x Time Equivalency Ratio.
40
28% higher,respectively, than the sole crops. ATER values
ait Bambey for grain and hay were close to 1.0 indicating
little difference in biological efficiency.
The magnitude of the partial LERs show which cultivar
made the major contribution to the total LERs. In 1988,
the partial LERs for grain (Table 12) were higher for the
early erect cultivars (Bambey 21 and CB5) at Bambey and
Thilmakha, whereas in 1989, the medium cycle cultivar had
the highest partial LERs in a11 locations. In X9 out of 24
cases, the partial LERs were greater than 0.5, indicating
contributions from both cultivars to the higher LERs of
the varietal intercrops (Table 12). Partial LERs for hay
(Table 13) indicated that in most cases both cultivars
contributed to the hi,;h LERs of the varietal intercrops at
Thilmakha and Louga in both 1988 and 1989.
The low par-
tial LERs for grain and hay during 1988 for the medium
cycle spreading cultivar at Bambey was partially due to
the high incidence of cowpea aphids and mosaic virus. The
data did not show a general suppression of partial LER in
the early erect cultivars, due to competition with the
spreading cultivar. The data in parentheses (Table 13)
demonstrated that the medium cycle spreading cultivar pro-
vided the major contribution to total hay yield in 1989 in
a11 locations, whereas in 1988 the early erect cultivars
contributed more to total yield. The data for grain exhi-
bited similar responses (Table 12).
41
8..
Table 12.
Partial LERs for grain for each component
cowpea cultivar in the varietal intercrop
during two years in each location.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*....
Location
Year
Intercrop treatments
58-57/Bambey 21
58-57/CB5
58-57
Bambey 21
58-57
CB5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*..........*......
1988
0.45 (39)'"
0.59
0.48 (35)
0.66
Bambey
1989
0.71 (54)
0.30
0.73 (59)
0.54
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1988
0.66 (46)
0.82
0.60 (31)
0.87
Thilmakha 1989 0.82 (57)
0.77
0.66 (63)
0.43
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1988
0.54 (58)
0.55
0.61 (48)
0.60
Louga
1989
0.62 (67)
0.48
0.75 (81)
0.58
. . . . . . . . . . . . . . . . . ..*................................*.*...
* Number in parentheses indicates the percent contribu-
tion of the medium cycle spreading cultivar (58-57) to the
total yield of the intercrop.
42
c
k
Table 13.
Partial LERa for hay for each component cow-
pea cultivar in the varietal intercrop
during two years in each location.
.~........................,...................”..........,,
Location
Year
Intercrop treatments
58-57/Bambey 21
58-57/CB5
58-57
Bambey 21
58-57
CB5
.,........................*.............m....
. . . . . . ..s....
1988
0.34 (313)*
0.55
0.39 (35)
0.78
Bambey
1989
0.66 (68)
0.50
0.76 (74)
0.80
. . . . . . . . . . ..e.....................
. . . . . . . . . . . . . .
1988
0.93 (43)
0.87
0.74 (46)
0.80
Thilmakha
1989
0.77 (57)
0.75
0.77 (73)
0.53
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1988
0.55 (42)
0.64
0.68 (38)
0.89
Louga
1989
0.69 (52)
0.84
0.85 (86)
0.22
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*.........*....~.*
* Number in parentheses indicates the percent contribu-
tion of the medium cycle spreading cultivar 58-57 to the
total yield of the intercrop.
The drought during the vegetative stage at Louga
(Figure 3) and Thilmakha (Figure 4) stressed the early
erect cultivars and could have been responsible for the
yield advantage of the la,te cultivar, 58-57, in 1989.
Mosaic virus infection could have contributed to the low
yield of 58-57 in 1988. This year-to-year variation in the
type of cultivar making the major contribution to total
yield illustrates the mechanism whereby varietal inter-
crops could have enhanced yield stability. Presumably, the
erect cultivars, which were early had completed podding by
the time the spreading cultivars encroached on their
space.
The year-to-year variation in partial LERs for
particular cultivars also illustrates the mechanism
whereby varietal intercrops could have stabilized yield
during the two years of studies.
Stabilitv and adaptation of the cultivars
Regression analysis was conducted on the mean yield
of each genotype in a given environment against an envi-
ronmental index consisting of the mean yield of a11 geno-
types in that environment (Tables 14 and 15). The high r2
values demonstrate that the linear regression was appro,-
priate. With respect to grain yield, the landrace 58-57
and the two varietal intercrops had the highest *lait value
(y intercept) and the lowest "bl' value (regression coeffi-
cient). This means that 'the late cultivar (58-57) and the
two varietal intercrops consisting of alternating rows of
44
Table 14.
Linear regression analysis over six environ-
ments (3 locations x 2 years) for treatment
grain yield versus environmental mean grain
yield in cowpea.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Treatment
Mean yield a
b
s.b.
r2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..".............
.
58-57
851
461
0.42
0.13
0.70
N'diambour
982
-48
1.10
0.13
0.95
Mougne
876 .
-81
1.02
0.15
0.92
Tvx 3236
950
-714
1.77
0.46
0.79
Bambey 21
931
-402
1.42
0.21
0.92
CB5
837
-64
0.96
0.32
0.69
58-57/B. 21
1018
446
0.61
0.22
0.65
58-57/CB5
1065
406
0.70
0.25
0.66
.
. . . . . . . . . . . . . . . . . . . ..a*...............
. . . . . . . . . . . . . . .
= Y intercept
b = coefficient of regression
s.b = standard error of the slope (b)
r2 = coefficient of determination
X = mean grain yield of each cultivar in each environ-
ment.
Y = mean grain yield of a11 cultivars in each environ-
ment.
45
.
.
Table 15.
Linear regression analysis over six environ-
ments (3 locations x 2 years) for treatment
. .
hay yield versus environmental mean hay
yield in cowpea.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Treatment
Mean yield
a
b
s.b.
r2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(kg/W
58-57
1729
-183
1.10
0.07
0.99
N'diambour
2069
-63
1.24
0.03
0.99
Mougne
1829
-141
1.15
0.03
0.99
Tvx 3236
1678
-447
1.24
0.02
0.99
Bambey 21
1441
293
0.67
0.09
0.94
CBS
1157
257
0.52
0.08
0.92
58-57/B. 21
1900
241
0.97
0.10
0.95
58-57/CB5
1926
46
1.10
0.05
0.98
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
= Y intercept
b = coefficient of regression
s.b. = standard error of slope (b)
r2 = coefficient of determination
X = mean hay yield of each cultivar in each environment.
Y = mean hay yield of a11 cultivars in each environment.
46
58-57 and Bambey 21 or CB5 were more stable and performed
better in the stress environment. However, the cultivar
58-57 had low mean yield whereas the two varietal inter-
crops had the highest mean yields. A more generalized
interpretation of varietal adaptation is'shown by plotting
the regression coefficient against the genotypic mean
yield (Figure 7). The varietal intercrops were well
adapted to a11 environments because they had the highest
mean grain yields. They also had low regression coeffi-
cients, indicating above average stability and better
adaptation to unfavorable environments (Finlay and Wilkin-
son, 1963). N'diambour was reasonably adapted to a11 envi-
ronments because of its high grain yield and its regres-
sion coefficient of 1.10, whereas 58-57 was only adapted
to the lower yielding environments with a regression coef-
ficient of 0.42. Tvx 3236 was very responsive to environ-
mental changes. With a regression coefficient of 1.77, it
is specifically adapted to favorable environments.
Results for hay (Table 15 and Figure 8) indicated
that a11 the treatments except the two erect cultivars
(Bambey 21 and CB5) had high potential for hay production
in that they had high hay mean yields and regression coef-
ficient close to unity. N'diambour and the two varietal
intercrops were best adapted to a11 environments in that
they the high hay yields and their regression coefficients
were around 1.0.
47
48
t
i
i
2 . 0
1.8
ATVX 3 2 3 6
1.6
5
Aa 21
w 1 . 4
u
2 1 . 2
w
bîûüGNE
g 1.0
A
A
0
cl35
z 0 . 8
58-57/CE5
w
A
58-57/B 214
L: 0 . 6
a
0 . 4
A 5 8 - 5 7
0 . 2
0.0 -
8 0 0
8 5 0
9 0 0
9 5 0
1 0 0 0
1050
1100
GENOTYPIC MEAN G R A I N YIELD [KG/HAj
.I,

al
50
r
i
P
#
2.0
i .B
i .6
t-
2 1 . 4
N’DIAMBOUR
u
(
t-i
T V X 3 2 3 6 .
MOUGNE
k t.2
A
w
5B--57
A
0
A
~58~57/C85
” 1.0
Ln
“m-57/8 2 1
P
0
u: 0 . 8
m
w
AB 21
go.6
%!
A Ci35
0 . 4
0 . 2
0.0 -1100 t
1
1
1
1 3 0 0
1 5 0 0
1 7 0 0
1 9 0 0
2ioo
GENOTYPIC MEAN H A Y
YIELD (KG/HA)
t
The spreading cultivars (Mougne and 58-57) and the semi-
erect cultivar (Tvx 3236) also had moderately high hay
production and their regression coefficients of 1.15,
1.10, and 1.24, respectively, indicated reasonable
sta-
bility. The two early-erect cultivars (Bambey 21 and CB5)
/.
were only adapted to unfavorable environments (low mean
grain yields and low regression coefficients). Their
small, erect, and determinate growth habit was incompa-
tible with high hay production. In summary, the linear
regression analysis showed that in terms of grain produc-
tion, the varietal intercrops were better adapted than the
cultivars grown as sole crops especially in the low yield-
ing environments, Thilmakha and Louga. In terms of hay
production, the varietal intercrops and N'diambour were
well adapted to a11 environments.
c
L
52
P
CONCLUSIONS
Intercrops of early-erect and medium-cycle spreading
cowpea cultivars were shown to be more effective than sole
c:rops of these cultivars in dry locations with infertile
soils in Senegal. In the Thilmakha and Louga locations,
farmers growing both types of cultivars would have to
plant 42 or 50% more land area of the sole crops to obtain
the same grain or hay yields as the varietal intercrops.
Farmers in these locations who are seeking the highest
yielding system should also choose the varietal inter-
crops. They had higher mean grain and hay yields than any
of the cultivars tested as sole crops, and above average
yield stability.
t
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